Solid state light sources may be utilized to provide colored (e.g., non-white) or white light (e.g., perceived as being white or near-white). A solid state lighting device may include, for example, at least one organic or inorganic light emitting diode (“LED”) or a laser. White solid state emitters have been investigated as potential replacements for white incandescent or fluorescent lamps due to reasons including substantially increased efficiency and longevity. Longevity of solid state emitters is of particular benefit in environments where access is difficult and/or where change-out costs are extremely high.
Because light that is perceived as white is necessarily a blend of light of two or more colors (or wavelengths), and light emitting diodes are inherently narrow-band emitters, no single light emitting diode junction has been developed that can produce white light. A representative example of a white LED lamp includes a blue LED chip (e.g., made of InGaN and/or GaN), arranged to stimulate a phosphor one or more phosphors (e.g., commonly yellow phosphors such as YAG:Ce or BOSE). A portion of the emissions of the blue LED chip pass through the phosphor, while another portion of such emissions is absorbed by the phosphor, which becomes excited and emits yellow emissions. The resulting mixture of blue and yellow light (sometimes termed ‘blue shifted yellow’ or ‘BSY’ light) may be perceived as cool white light. Various methods exist to enhance cool white light to increase its warmth, including supplementation with a red LEDs or red phosphor. Additional or different supplemental LEDs and/or phosphors (e.g., of other colors) may be used. Various methods exist for arranging lumiphoric materials (e.g., phosphors) to be stimulated by solid state emitters, including coating of one or more lumiphoric materials directly on a surface of a solid state emitter chip, or combining one or more lumiphoric materials with a binder and depositing the combination over one or more solid state emitter chips (e.g., mounted on a substrate or in a reflector cup). One or lumiphoric materials may also be associated with an optical element such as a lens that is positioned on or over a solid state emitter chip.
Various solid state lighting devices including optical elements and/or lumiphoric materials arranged in discrete layers or regions are disclosed in U.S. Patent Application Publication No. 2009/0039375 A1 to LeToquin, et al. and U.S. Pat. No. 7,709,853 to Medendorp, Jr., which are commonly assigned to the owner of the present application and are hereby incorporated by reference as if set forth fully herein. U.S. Pat. No. 7,709,853 discloses use of multiple layers of materials (e.g., silicone, epoxy, hybrid silicone/epoxy materials) having different indices of refraction. U.S. Patent Application Publication No. 2009/0039375 A1 further discloses texturing or patterning of an overlayer along an outer light emitting surface thereof in order to increase light extraction.
A technical paper by Ma, et al., Opt. Express, Vol. 19, No. S5. (September 2011), pp. A1117-A1125, entitled “Effects of the refractive index of the encapsulant on the light extraction efficiency of light-emitting diodes” (“Ma et al.”) discloses use of a dual-layer graded refractive index encapsulant with a light emitting diode chip to reduce Fresnel reflection at the encapsulant/air interface (e.g., by 35% compared with a LED encapsulated with a single-layer encapsulant).
Although lighting devices including multiple encapsulant layers are known, various improvements to lighting devices including multiple encapsulant layers would be desirable. It would be desirable to enhance adhesion between such layers or regions. It would also be desirable to facilitate greater control of optical properties (including, but not limited, focus and/or directionality) of lighting devices including encapsulant materials. It would further be desirable to enhance color mixing of, and/or increase light extraction from, lighting devices including encapsulant materials. Various embodiments as disclosed herein address or more of the foregoing concerns.